The position of the gastrocnemius tendon relative to the calcaneus and fibular head distance may be different in children with cerebral palsy (CP) when compared to normal children. However, no such data is available. Usually, palpation of the muscle bellies or previous experience of the operating surgeon is employed to place the surgical incision. Inaccurate localisation may cause incorrect incision and a risk of iatrogenic damage to the vital structures (i.e. sural nerve). The aim of our study is to compare gastrocnemius muscle length in-vivo between paretic and unaffected children and suggest a formula to localise muscle-tendon junction.

Ten children with di/hemiplegia (seven females and three males; mean age 8y 7mo, range 2–14y) were recruited. None of them had received any conventional medical treatment. An equal number of age/sex matched, typically developing children (mean age 9y 1mo, range 4–14y) were recruited. Participants lay prone on an examination plinth with their feet hanging from its edge. Sagittal-plane ultrasound scanning of the gastrocnemius muscle at rest was performed to measure the length of gastrocnemius bellies. We also measured the heights, lower leg lengths, thigh lengths and leg lengths.

At similar age, the lower leg lengths in CP patients were shorter than normal children. Similarly, gastrocnemius medial (GM) muscles were shorter in CP children when compared to similar aged normal children. In CP children, the GM muscle and lower leg ratio ranges between 35 to 50% with an average ratio of 45%. When compared to leg length, the ratio is 22%.

Using these figures we created a formula that may be used clinically to identify the tendon for open or endoscopic lengthening and also to make simple and accurate localisation of GM-tendon junction for surgical access. This minimizes the risk of iatrogenic neurovascular injuries and decreases the length of the surgical incision.